Electricity and other forms of energy are billed in accordance with energy consumption that may vary with the size of the customer and the time of day. Since the peak amount of energy consumed by a customer over a given time period (so-called "demand") determines the size of the service required, e.g. size of conductors, transformers, peak generating capacity, etc., many utilities measure this peak consumption or demand to determine the rate to be charged the customer for all electricity consumed over a given period.
To determine the amount of energy being consumed by each customer during successive demand intervals, utility companies have located, at customer sites, electricity meters, such as watthour meters containing a demand register, which must periodically be read either by the customer or by a representative of the utility, to accumulate billing data (e.g. peak demand and total energy consumed). In addition, to evaluate customer energy demand so as to assess the capability of the utility's equipment to satisfy demand, or to justify rate modification, energy demand occasionally must be surveyed over an extended period of time, e.g. 18 months.
Electrical demand is typically measured by the use of a pulse initiator which utilizes a photo-optical detector to detect the rotation of the eddy-disk of a watt-hour meter and produces a series of pulses whose frequency is directly related to the instantaneous power (demand) being delivered to the customer.
Typically, a demand register accumulates these pulses over a preselected interval, e.g. 15 minutes, to give an indication of the peak demand over the interval. This peak demand data is then stored in a memory device for subsequent readout or display.
Since there will often be large numbers of meters registering demand throughout a utility system there exists a need to monitor electrical demand simultaneously at a large number of individual customer sites, and to process the data at a central location. This is commonly done by means of a mainframe computer operated by the utility company. This information is used by the utility to assess demand parameters such as peak demand and seasonal as well as daily demand variations. Accordingly, systems have been developed for polling customer meters to extract and transmit energy demand data over commercial telephone lines to the central computer for accumulation and processing.
Because the investment required to provide automatic polling of remote meter registers at the customer site is substantial, as an alternative, automatic meter data recorders have been developed that are set up at customer sites to be monitored. The data recorders commonly employ magnetic tape storage techniques to record pulses generated by the pulse initiator of the meter that represent electrical demand during successive intervals. The magnetic tape is then carried to the utility for processing.
Magnetic tape recorders of the type employed for this purpose are relatively complex, require substantial battery power to operate in the event of a power failure and may fail to work properly in environments exposed to temperature extremes. Recently, due in part to availability of inexpensive solid state memory devices, portable meter reading devices having solid state memories have been developed for accumulating demand data stored in a meter. The reading device is then either brought to the central computer and the data transmitted directly to the computer, or the data is transmitted over telephone lines to the central computer. There is a tendency, however, for errors to occur in the acquisition and transmission of data. These errors are caused by among other things failures of the solid state memory, misdetection of pulses generated by the electricity meter and, most commonly, electrical noise contamination. Data acquisition errors are particularly troublesome because they affect, among other things, the accuracy of customer billing. For this reason there currently exists a significant need to verify energy demand data accumulated from customer meters to ensure that the data is accurate. Also, since peak demand data must be correlated with the time of day, day-of-week, season, etc. for proper billing purposes, it is necessary that such a data acquisition device be capable of operation despite power outages occurring on the power line.
In systems which employ battery back-up power supplies for operation in the event of a power failure, there exists a need for determining when the battery has grown weak and requires replacement. Problems can occur in accumulating and maintaining verifiable energy demand data if the battery back-up system fails to provide a reliable alternative source of power during power outages. If the back-up battery has become marginal or failed (especially during periods of frequent outages), the recorded customer demand data may be erroneous or suspect. Yet, the utility has no way of determining when the back-up battery failed so as to estimate the beginning of the suspect data. Prior to the present invention, there has been no known way to accurately monitor the performance of battery back-up systems short of regular planned replacement at periodic intervals in accordance with known statistical replacement techniques, or periodic on-site testing of the batteries at the customers' facilities.
Other problems have been encountered in conventional remote meter data recorders which transmit energy demand data over commercial telephone lines to a central computer for processing. Because of this preexisting communications link for meter data collection, it would be economically advantageous to use the same equipment for energy management functions, such as where customer loads are interrupted during periods of peak demand. However, such prior art data recorders are configured to transmit the energy demand data to the central computer only at predetermined times. These predetermined times are usually selected when a customer's telephone line is not likely to be in use, e.g. during the late night hours. This type of prior art data recorder can receive command information from the central computer over the telephone line only after the recorder has initiated the communication by dialing up the central computer to download its data. Systems which can receive commands only during recorder-initiated communication modes are not receptive to receipt of commands at any time other than when communication has been initiated by the recorder, and are therefore unable to provide energy management functions.
Still other problems have been encountered in data recorder systems which are receptive to commands only after initiation of a communication by the meter for the purpose of downloading data. In particular, there exists a need for detection of error conditions such as power outages, low battery condition, or a malfunction in the meter. Conventional meters and recorders which are unable to provide indications of error conditions have proven unsatisfactory to electrical utilities which need to be able to monitor and correct error conditions rapidly and to perform peak load energy management functions.
One object of the invention, therefore, is to provide a method of and system for verifying data accumulated from remote electricity meters during successive demand intervals and to confirm that the data measured represents data upon which a utility company or other controlling institution can rely. Another object is to provide a relatively inexpensive and reliable device for making energy demand measurements and verifying their reliability at customer meter sites for the purpose of obtaining demand survey and customer billing data. A further object is to provide an electricity demand data acquisition device which operates reliably even during a power outage.
Another object of the present invention is to provide an electricity demand acquisition device which initiates a communication to a central computer in the event of an error condition such as a power outage, low battery condition, or malfunction in the metering device.
It is another object of the present invention to provide an electricity demand data acquisition device which is operative to override the conventional data downloading operational sequence (which occurs at a predetermined time) and receive communications initiated by the utility central computer.
It is another object of the present invention to provide an electricity demand data acquisition device which may be configured for operation over a wide range of utility customer demands by scaling the KYZ pulse input.
It is another object of the present invention to provide an electricity demand data acquisition device which maintains an indication of the time of day and date of the occurrence of a low battery condition so that an estimation of the reliability of the data stored in the device can be made.